This invention relates to polyurethane foams which exhibit decreased aldehyde emissions, a process of making these foams with decreased aldehyde emissions and a method of decreasing aldehyde emissions in polyurethane foams.
Aldehyde exposure limits, including limits specifically for formaldehyde and acetaldehyde, have been assigned by NIOSH and OSHA. These exposure limits are of significant interest to the Automobile and slabstock industries in the overall efforts of these industries to enhance the air quality of the auto-cabin and of bedding materials. End users of automobiles and bedding materials are exposed to any excess VOCs (volatile organic compounds), including aldehydes, that may be emitted from the foams.
From previous studies it is known that both foams and the polyether polyols used to produce foams emit aldehydes when heated in the presence of air. Thus, most polyurethane foams and processes for producing these foams will result in the emission of aldehydes.
Japan Automobile Manufacturers Association (JAMA) has identified several VOCs, including formaldehyde and acetaldehyde, as contributors to the so-called “sick-house syndrome”. Increasingly, it is common for automotive foams to be required to pass the Toyota test, i.e. the TSM0508G test, and for slabstock foams to pass the CertiPUR/LGA/-EUROPUR/IKEA tests. Foam products in Europe which satisfy one or more of these tests may be given a seal or stamp to indicate this. Thus, it is not uncommon in Europe for customers to look for foam products which bear these seals or stamps.
Various approaches for reducing aldehyde emissions have been tried. U.S. Published Patent Application 20080281013 discloses that aldehyde emissions in heated storage of a polyurethane resin can be reduced by including at least one sulfurous compound in the polyol component which is used to prepare the polyurethane resin. Suitable sulfurous compounds are selected from the group consisting of hydrogen sulfites and disulfites. Typically, from 0.02 to 2 parts by weight of sulfurous compounds are added for every 100 parts of the polyol component.
Any manufacturer that can make and/or sell polyurethane foams that can pass these stringent requirements, particularly with respect to aldehyde emissions, has a significant competitive advantage over their competitors. New ways of reducing aldehyde emissions and lowering the exposure of end-users and customers to these emissions are highly desirable in the industry.
A reactive system and a process for reducing free MDI emissions in cavity filling NVH polyurethane foams is disclosed in U.S. Pat. No. 7,678,840. These systems comprise a polymethylene poly(phenyl-isocyanate) which has a polymeric MDI content of greater than 70% by weight and a monomeric MDI content of less than 30% by weight, and the monomeric MDI is comprised of less than or equal to 25% by weight of the 4,4′-isomer, less than or equal to 5% by weight of the 2,4′-isomer and less than or equal to 2% of the 2,2′-isomer. These reactive systems are suitable for acoustic foams and structural foams which have reduced isocyanate emissions, i.e. decreased quantities of free MDI.
U.S. Published Patent Application 20080125507 discloses reactive systems and a process for reducing VOC (volatile organic compound) emissions from low density cavity filling NVH polyurethane foams. These reactive systems comprise (A) a polymethylene poly(phenylisocyanate) having a polymeric content of greater than or equal to 55% by weight, and a monomeric content of less than or equal to 45% by weight; and (B) an isocyanate-reactive component comprising (1) at least one isocyanate-reactive compound having a molecular weight of from about 1,000 to about 10,000, a functionality of from about 2 to about 6 and an OH number of from about 10 to about 340; and (2) at least one isocyanate-reactive compound having a molecular weight of from about 60 to less than 1,000, a functionality of about 2 to about 4, and an OH number of from about 110 to about 3750; wherein at least one of (B)(1) and (B)(2) comprises an amine-initiated compound; in the presence of (C) at least one catalyst; and (D) a blowing agent comprising water.
Foams having reduced visible emissions during curing are disclosed in U.S. Pat. No. 5,373,028. These foams are prepared from a formulation comprising (a) a polyisocyanate, (b) an isocyanate-reactive component, (c) a visible emissions producing component, and (d) a visible emissions reducing agent, with these components being reacted under conditions to form a polyurethane and/or polyurea foam and the foam is cooled, wherein visible emissions are emitted during the cooling. The presence of (d) the visible emissions reducing agent in the foam formulation results in lower amounts of visible emissions being emitted from the foam during curing. Antioxidants are described as visible emissions producing components. Suitable visible emissions reducing agents disclosed are (a) alkali metal dihydrogen phosphates and polyphosphates, (b) alkali metal sulfates, (c) aluminum sulfates, phosphates, polyphosphates, borates and alkanoates, (d) ammonium sulfates, phosphates, polyphosphates, borates and alkanoates, (e) acid chlorides, and (f) mixtures thereof.
Filled polyols are known and described in the art. These filled polyols are typically polyether polyols that are “filled” with other organic polymers to produce viscous, white to off-white, fluids that are suitable for preparing foams with increased (i.e. higher) hardness levels that conventional, unmodified polyols can produce. In general, filled polyols are prepared by in situ polymerization of one or more monomers in a polyol base, using either free-radical or step addition processes. Common types of filled polyols include styrene-acrylonitrile polymer polyols (i.e. SAN polymer polyols), polyhydrazondicarbonamide (i.e. PHD) polyols, and polyisocyanate polyaddition polyols (i.e. PIPA polyols).
PHD polyols or polyhydrazodicarbonamide polyols that comprise the reaction products of (a) one or more polyisocyanates, with (b) one or more hydrazines, polyamines, dihydrazides, ammonia, urea, and/or low molecular weight polyols, and (c) optionally higher molecular weight polyols, and (d) optionally, formaldedhyde, in the presence of one or more polyhydric alcohols having a molecular weight of between 62 and 450, and described in U.S. Pat. No. 4,324,716. These dispersions have solids contents of from about 5 to 70% by weight, and are clear, storage stable solutions with a relatively low viscosity. In the examples of this reference, the foams are prepared from conventional polyether polyols and PHD polyols. Reducing the emissions of aldehydes in foam products is not disclosed or mentioned in U.S. Pat. No. 4,324,716.
Although various approaches have been taken to reduce different types of emissions from polyurethane foams and/or polyurea foams, none of the prior approaches includes the addition of small amounts of trimerized hexamethylene diisocyanate to the polyisocyanate component, or small amounts of a polyhydrazodicarbonamide dispersion to the isocyanate-reactive component. It is an object of the present invention to reduce aldehyde emissions in foam products
Advantages of the present invention include the ability to form foam products with reduced aldehyde emissions by the addition of low levels of trimerized hexamethylene diisocyanate to the polyisocyanate component, or small amounts of a polyhydrazodicarbonamide dispersion polyol to the isocyanate-reactive component, and the ability to product foam products that comply with different regulation emissions as described above.